On Feb 17, 2010, at 8:55 AM, David Winsemius wrote:
On Feb 17, 2010, at 8:26 AM, Ista Zahn wrote:
Hi all,
I am designing a study in which I am selecting a subset of college
courses to be randomly assigned to one of two conditions. I would
like
to create matched pairs of courses, and then randomly assign them to
condition within each pair. I would like to identify, for each
course,
the one that best matches it, and quantify how well it matches. Here
is a much simpler data set for purposes of illustration:
ED <- data.frame(course = letters[1:5], level=factor(c(100, 100, 200,
300, 200)), size = c(44, 12, 23, 124, 30), rating = c(4,5,5,3,5))
course level size rating
1 a 100 44 4
2 b 100 12 5
3 c 200 23 5
4 d 300 124 3
5 e 200 30 5
> ED$grps <- paste(ED$level, cut(ED$size,
breaks=c(0,15,35,60,150,300)),
+ cut(ED$rating, breaks=c(0,2,4,6)), sep=".")
> ED[order(ED$grps), ]
course level size rating grps # forgot to relabel
2 b 100 12 5 100.(0,15].(4,6]
1 a 100 44 4 100.(35,60].(2,4]
3 c 200 23 5 200.(15,35].(4,6]
5 e 200 30 5 200.(15,35].(4,6]
4 d 300 124 3 300.(60,150].(2,4]
I got an offlist request to explain this. I see that I fail to
properly edit it so that the 5th column was named "grps". I had run
the function originally to create ED$cuts, but thought that variable
might be better called "grps" so edited the functions but failed to
edit the output. If the question what how it works, then:
A) create grouping categories for each variable. I applied my domain
knowledge to decide that levels ought to be "ungrouped" but that size
and rating would be groups in categories that were determiend by the
breaks argument to the cut functions.
B) paste the together with a "." period separator to create "grps"
that would be considered similar. This I believe is "blocking" in
anova terminology and perhaps "strata" in regression terminology. The
category labels become just parts of the bigger character string.
--
David.
Basically I want a function that tells me that courses c and e
"match"
so that I can treat them as a pair and randomly assign them to
condition. I've looked at the matching and MatchIt packages, but they
seem to need to know in advance which course is in the treatment
condition and which is in the control condition. I'll be grateful for
any suggestions.
Best,
--
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
